It was in development for the PS2 since 2004, but then Rockstar Vienna shut down...and now the game has been revived by Rockstar London. Basically, they want this game to come out late Spring/early Summer and the only way they can do that is if they release it on last generation's hardware (PS2, PSP). Wii is very similar graphically and in terms of processing power to the PS2, so it would be easy to port the game to there (and adding in stuff for the WiiMote shouldn't be difficult either).